1. Field of the Invention
This invention relates to plasma display devices and more particularly to an improved means for conditioning such devices prior to a write operation.
2. Description of the Prior Art
The use of a light source designated a pilot light to facilitate discharge of a plasma display device is well known in the art, and is disclosed, for example, in U.S. Pat. No. 3,609,658, "Pilot Light Gas Cells for Gas Panels" issued to Parviz Solton Sept. 28, 1971, hereinafter designated the '658 patent. The device disclosed in the '658 patent employs one or more light sources designated pilots incident to the panel. While the theoretical physics of the operation of a plasma device is not universally accepted, it is believed that the photons emitted by the pilot cell or cells provide or activate the charge particles necessary for discharge, thereby conditioning the panel for a write operation.
Despite an independent power supply, it was discovered that the pilot in the '658 patent had an inherent starting problem, particularly in a dark environment, or after it had not been ignited over an extended period. This problem was solved by using a small radioactive source such as Nickel 63 positioned in the vicinity of the pilot cell which emits beta radiation sufficient to facilitate initial firing of the pilot cell when a drive signal was applied thereto. This teaching is embodied in U.S. Pat. No. 3,928,781 "Gaseous Discharge Display Panel Including Pilot Electrodes and Radioactive Wire" issued to Roger Joseph Edwards et al. Dec. 23, 1975, hereinafter designated the '781 patent. Both of the above referenced patents are assigned to the assignee of the instant invention.
While the above described '781 operation was adequate for smaller size lower resolution panels, the time at which the various electrodes were conditioned for a write operation varied as some functions of the distance from the pilot cells which were positioned either at the corner or on horizontal rows above and/or below the viewing area of the panel. The cells farthest from the border took longer to condition than those adjacent the border such that optimum write pulse timing varied as a function of distance from the border. In small gas panels such as those described in the '658 and '781 patents, the use of a pilot configuration above and below the data area and the relatively small data areas allowed this variation in conditioning times to be tolerated. However, in panels of substantial size and high resolution, faster update times are required and the piloting action was substantially inferior in the center of the panel when well timed for the edges and vice-versa. This situation could not be tolerated, since practical addressing systems are based on all cells having the required conditioning simultaneously. Finally, disposal of panels containing the radioactive wire disclosed in the '781 patent was covered by Federal and/or state regulations, further adding to the cost of the device.